This proposal is for support of a Postdoctoral Research-Training Program in Infectious Diseases. The program is structured to primarily train physicians, who have completed at least one year of clinical training in Infectious Diseases, as well as individuals with a PhD who wish to pursue postdoctoral studies in Infectious Disease research. Two or three years of support for scientific training are requested depending on the prior research experience of particular individuals. The training program faculty is drawn from scientists in the Division of Geographic Medicine and Infectious Diseases and the Clinical Care Research Center at the New England Medical Center as well as from the Basic Sciences Departments of Irnmunology and Molecular Biology and Microbiology at the adjacent Tufts University School of Medicine. The program is focused on studies relevant to the clinical implications of the Host-Pathogen Interaction. The program's themes are 1) Investigation of virulence determinants of viral, bacterial, fungal and protozoan pathogens, 2) Investigation of host responses to these pathogens and 3 ) Epidemiological analysis of factors that impact clinical outcomes of host-pathogen interactions. While this grant proposal is for support of five postdoctoral fellows per year, there are in aggregate, over 100 post-doctoral fellows and pre-doctoral students in training with the program faculty at this time. This establishes a rich academic environment in which MD's and Ph.D.'s interact closely. Each trainee works under the close supervision of a faculty mentor and is supported by a Personal Progress Review Committee (PPRC). Academic enrichment includes didactic courses in bio-statistics, biochemistry, molecular biology, immunology, cell biology and microbial pathogenesis. All fellows attend seminars in ethics and scientific integrity. Weekly conferences include a research-in-progress seminar, journal club and several invited speaker seminar series in Immunology, Molecular Biology and Microbiology and Clinical Epidemiology. The laboratory and computer facilities available to the trainees are extensive and up to date. The core of the program is supervised research under the guidance of well-funded faculty members with deep commitment to and experience in training future independent investigators. The fundamental goal of the program is to train the next generation of academic scientists contributing to the understanding and treatment of infectious diseases.